This invention relates to a disconnect switch for metal-encapsulated switching installations. Such switches have a fixed tubular contact engaged by a movable contact tube which is guided in a stationary outer part. Inside of the movable contact tube there is an auxiliary contact which is movable relative thereto, which is acted upon by a spring, and which connects to a fixed auxiliary contact forming part of the stationary contact.
A disconnect switch of this type, described in Siemens Operating Instructions SW 8378-220 "Load Disconnect Switch 3CB, 10 kV," pages 102/1 to 102/3, is designed as a load disconnect switch (circuit breaker) and has an auxiliary contact pin which, during the switching-off movement, permits formation of an arc only between a so-called sliding contact and a burn-off ring of the movable contact because this arc frees gas from the insulating material of the stationary outer part; the gas escapes from the quenching cup in a strong flow, deionizing the switching gap. Since a quenching device is not provided between the fixed contact and the moving contact in this load disconnect switch, a metallic connection must be maintained between these two contact elements during switching off via an auxiliary contact, until the switching path is interrupted after the arc is extinguished. The auxiliary contact is then pulled out of contact with the auxiliary part of the fixed contact so that the disconnect switch is visibly separated.
It is an object of the present invention to provide a disconnect switch of the above type which can be used at higher voltages and which has short pre-breakdown times with the large switching gaps required in such structures, without necessitating a particularly fast-operating drive. Pre-breakdown time is to be understood here to mean that time during which an arc occurs between the fixed contact and the movable contact in the switch opening process.